linux-kernel - Re: [PATCH 1/2] ASoC: dmaengine_pcm: Add support for packed transfers

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Date:	Wed, 27 Apr 2016 16:33:12 +0200
From:	Martin Sperl <kernel@...tin.sperl.org>
To:	Matthias Reichl <hias@...us.com>
Cc:	Lars-Peter Clausen <lars@...afoo.de>,
	Jaroslav Kysela <perex@...ex.cz>,
	Takashi Iwai <tiwai@...e.com>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>, alsa-devel@...a-project.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] ASoC: dmaengine_pcm: Add support for packed transfers


> On 27.04.2016, at 15:26, Matthias Reichl <hias@...us.com> wrote:
> 
> dmaengine_pcm currently only supports setups where FIFO reads/writes
> correspond to exactly one sample, eg 16-bit sample data is transferred
> via 16-bit FIFO accesses, 32-bit data via 32-bit accesses.
> 
> This patch adds support for setups with fixed width FIFOs where
> multiple samples are packed into a larger word.
> 
> For example setups with a 32-bit wide FIFO register that expect
> 16-bit sample transfers to be done with the left+right sample data
> packed into a 32-bit word.
> 
> Support for packed transfers is controlled via the
> SND_DMAENGINE_PCM_DAI_FLAG_PACK flag in snd_dmaengine_dai_dma_data.flags
> 
> If this flag is set dmaengine_pcm doesn't put any restriction on the
> supported formats and sets the DMA transfer width to undefined.
> 
> This means control over the constraints is now transferred to the DAI
> driver and it's responsible to provide proper configuration and
> check for possible corner cases that aren't handled by the ALSA core.
> 
> Signed-off-by: Matthias Reichl <hias@...us.com>

Tested-by: Martin Sperl <kernel@...tin.sperl.org>